Dodders come by many names. What to know about the plants in Ohio

Call it strangleweed, wizard's net, devil's guts, hellbine or witch's hair…or, if you prefer, lady’s laces, angel hair, goldthread or love vine.

It’s all the same to Cuscuta gronovii, a plant more often referred to these days as common dodder or swamp dodder. But why all the bizarre folk names, like something out of a witch’s bubbling cauldron?

Plant has no leaves or roots

Interesting plant. In fact, you might never guess that the golden tangle of string seemingly cast randomly on the chrysanthemums and dahlias in the garden, or draping over alfalfa, clover and potatoes in a neighboring field is even a plant. There’s nothing green about it and you won’t find leaves or roots.

Well, actually, dodder does have leaves, but they’re reduced to barely visible scales, and the tiny cluster of rootlets found on a newly germinated seed disappear soon after the threadlike shoot finds a victim.

Or “host,” if you want the technical term, but there’s no denying that dodder is one of the vampires of the plant world. Biologists refer to plants like dodder that get most or all of their nutrition from other plants as parasites. And the way dodder manages to find and parasitize an appropriate host plant provides one of the clearest examples of plant behavior that I know of.

We tend to think of behavior as something that only animals are capable of. Plants and fungi don’t have a brain or nervous system, and therefore they can’t intentionally move their body parts to achieve some goal. But is that really the case?

The tricky word in that last paragraph is “intentionally.” Dandelions, tulips and poppies, among many other plants, close their flowers at night. It’s thought this may protect the reproductive parts from being chewed on by nocturnal insects or getting soaked with dew.

After opening in the morning, common daisies track the sun as it moves across the sky, a trait thought to enhance pollination and fertilization. In fact, in addition to growing roots, branches and flowers, the ability to manipulate various parts of the body in useful ways is seen in a lot of plants.

Ohio has 13 types of dodders

Even if a dandelion doesn’t “know” why it closes up at night, doing so is a form of goal-oriented movement that sounds like intentional activity to me, and I’m happy to think of it as part of the dandelion’s behavioral repertoire. So, getting back to dodders, let’s look more closely at what we might reasonably call the plants’ foraging behavior.There are some 150 to 200 species of dodder (depending on the taxonomist you consult), 13 of which occur in Ohio. The most common one here and across most of the U.S. is the C. gronovii.

Dodder seeds drop to the ground when mature or can be dispersed more widely by the wind, by animals brushing up against the plant or by human agricultural practices. In the spring, the 16-inch-long seed sprouts on the surface of the soil and sends out an exploratory shoot. It only has five to 10 days to find a suitable host before using up its small store of food reserves.

Here’s where things get interesting. Although dodders typically parasitize a wide variety of plant hosts, each species does better when feeding on certain hosts than others. In 2006, researchers reported that seedlings of the five-angled dodder (a close relative of the common dodder) use volatile compounds secreted into the air by various plants as hunting cues.

Dodders tend to like tomato plants

When exposed to gases released by both a tomato plant, a preferred host, and wheat, a non-host, the dodder grew toward the tomato.

After attaching itself to an appropriate host, a dodder shoot wraps itself around it and produces a series of small structures called haustoria that insert themselves into the vascular system of the host, where they will draw out nutrient-rich fluids to support the dodder as it grows, branches off new filaments and develops its reproductive structures.

In northern parts of the world, dodders are annuals that must produce new seedlings each spring and are therefore largely restricted to low vegetation. However, in the tropics, many dodder species are perennials that over time can grow right up into the canopies of trees.

The different species of dodders vary in how lethal they are to their hosts, but all infestations weaken their hosts’ ability to resist viral disease and the fact that dodders can transmit an infection from one host plant to another can make them a serious agricultural problem.

We’re just beginning to learn some of the ways host species defend themselves against being parasitized by dodders. For instance, those masses of tiny hairs (called trichomes) lining the stems of a tomato plant have been shown to interfere with the parasite’s ability to latch onto the stem.

Ken Baker is a retired professor of biology and environmental studies. If you have a natural history topic you would like Baker to consider for an upcoming column, please email your idea to[email protected].